1. Field of the Invention
The present invention relates to a vapor controller capable of quantitatively vaporizing liquid materials, such as silicon tetrachloride (SiCl.sub.4), used in for example an apparatus for producing semiconductors.
2. Description of the Prior Art
In one of the conventional vapor controllers, as shown in FIG. 12, a liquid material tank 82 housing a liquid material LM therein is provided within a thermostatic oven 81 suitably set in temperature, said liquid material tank 82 being suitably heated by means of a plate heater 83 to rise a temperature within the liquid material tank 82, whereby increasing a vapor pressure of said liquid material LM to vaporize the liquid material LM, and a vaporized gas G being directly controlled in flow rate by means of a gas mass flow controller (hereinafter referred to as GMFC) by obtaining a differential pressure relative to an outlet side.
In addition, in another example of the conventional vapor controllers, as shown in FIG. 13, a vaporizing chamber 93 filled with powdery substances 93 superior in thermal conductivity and corrosion resistance is formed within a metallic block 91 including a heater (not shown) therein, said vaporizing chamber 93 being provided with a liquid material supply line 94 for introducing the liquid material LM thereinto and a carrier gas supply line 95 for introducing a carrier gas CG thereinto connected with one end side thereof, the upstream side of said liquid material supply line 94 being connected with a liquid material tank 98 through a liquid material mass flow controller (hereinafter referred to as LMFC) 96 and a stop valve 97, and said liquid material LM, which has been controlled in flow rate by means of said LMFC 96 under the condition of liquid material, being introduced into the vaporizing chamber 93 to vaporize the total quantity of the liquid material LM. In addition, reference numeral 99 designates a thermostatic oven and reference numeral 100 designates an inert gas-introducing pipe.
However, in said vapor controller shown in FIG. 12, a disadvantage has occurred in that it is necessary to heat the whole liquid material tank 82 and the liquid material LM is always influenced by heat, so that not only a thermal decomposition and a change in composition are brought about but also impurities are dissolved out of the liquid material tank 82 to mix in the liquid material LM. In addition, in the vapor controller shown in FIG. 12, a disadvantage has occurred in that a gas flow rate is directly controlled, so that a time from a start of generation of gas to a stabilization of flow rate is greatly dependent upon a performance of said GMFC 84 and thus the GMFC 84 of high performance characteristics so much as that must be used and consequently cost is increased. In addition, a vapor pressure at an appointed heating temperature is low in dependence upon different kinds of liquid material LM according to circumstances, so that it has been necessary to reduce a pressure-drop of the GMFC 84 as far as possible.
Furthermore, in said vapor controller shown in FIG. 13, inert gases, such as nitrogen and helium, are supplied in said liquid material tank 98 to increase a pressure within the liquid material tank 98, whereby sending the liquid material LM to the side of the vapor controller under pressure by a supply pressure, so that said inert gases used for pressurizing the liquid material LM within the liquid material tank 98 is dissolved in the liquid material LM according to circumstances and consequently the liquid material LM is supplied to the vapor controller under the condition that dissolved gases are included.
And, when a local pressure-drop is produced in the LMFC 96 provided in the liquid material supply line 94, said dissolved gases in the liquid material LM are released into the liquid material supply line 94 (this is called a cavitation). In such the manner, the gases released into the liquid material supply line 94 are turned into very small bubbles but there is the possibility that these bubbles are collected in a stand of the supply line and the like to intermittently and periodically introduce larger bubbles into the vaporizing chamber 93. Consequently, vapors led out of the vapor controller comes into question according to circumstances in respect of stability of flow rate. In the case where the secondary side (downstream side) of the vaporizing chamber 93 is vacuous, this phenomenon becomes more notable. That is to say, because not only the dissolved gases but also the liquid material LM are vaporized in the liquid material supply line 94.
Moreover, in the vapor controller shown in FIG. 13, a disadvantage has occurred in that the vaporizing chamber 93 is filled with said powdery substances 92, so that a pressure-loss is produced within the vaporizing chamber 93 to take a time until a pressure rising during a time when the liquid material LM controlled by means of the LMFC 96 is introduced into the vaporizing chamber 93 to be vaporized is brought into an equilibrium condition within the vaporizing chamber 93 and thus a response as the gas flow rate becomes deteriorated.
Besides, in the case where the liquid material LM has a high reactivity, for example the liquid material LM acts upon water in air to produce reaction products, it has been necessary when parts of the vapor controller in trouble are exchanged that the liquid material is sufficiently removed from an inside of a pipe of a liquid material-introducing passage formed within the vapor controller to avoid a formation of reaction products as far as possible. In order to remove the liquid material remaining in said pipe, methods, such as gas purge, liquid purge or vacuum exhaust, have been used but it has been necessary that a purge gas is sent into the vapor controller from the upstream side of the vapor controller by means of a pump provided on the downstream side of the vapor controller for exhausting from a chamber of the apparatus for producing semiconductors to conduct said gas purge and said vacuum exhaust and the purges are conducted through the vapor controller, so that a pressure-loss is increased and thus it has been difficult to obtain a sufficient purge efficiency. The similar matters hold good in case of said liquid purge.